Secondary battery and electric equipment

Abstract

The invention provides a secondary battery and electric equipment. The secondary battery comprises a positive pole piece, an electrolyte, an isolating membrane and a negative pole piece, the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, and a positive active substance in the positive active material layer comprises a mixture of lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and a manganese ion complexing agent; the positive pole piece meets the condition that 10000 * W1 * PD / pH2 * W2 is more than or equal to 0.10 and less than or equal to 3.0; in the formula, W1 represents the mass ratio of the manganese ion complexing agent in the positive electrode active material; w2 represents the mass ratio of lithium manganese iron phosphate in the positive electrode active material; pD g / cm < 3 > represents the compaction density of the positive pole piece; and pH represents the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25 DEG C. By adjusting the parameters of the positive pole piece, the secondary battery has relatively high energy density, a charge-discharge voltage platform and stable circulation.

Description

Technical Field

[0001] The present application relates to the field of battery technology, in particular to a secondary battery and an electrical device. Background Art

[0002] With the rapid development of electric vehicles, the market now has higher and higher requirements for the durability, safety and cost of lithium-ion batteries. Lithium iron phosphate (LiFePO4) has an olivine structure and has the advantages of high safety performance, good cycle performance, and good thermal stability. It is widely used in lithium-ion secondary batteries as a positive electrode active material. However, due to the low charge and discharge voltage of its Fe element and the low voltage platform, its energy density is relatively low. Lithium manganese iron phosphate (LiMn x Fe 1-x PO4), the doping of manganese element can increase the charging and discharging platform voltage of lithium-ion secondary batteries and have a higher energy density.

[0003] But Mn 3+ ions are prone to undergo the Jahn-Teller effect and thus undergo disproportionation reaction to generate Mn 2+ and Mn 4+ ; and Mn 2+ It is easy to dissolve from the positive electrode surface and react with the electrolyte to cause the decomposition of the electrolyte. In addition, the precipitated Mn 2+ It will reach the negative electrode through the electrolyte, causing the destruction and reorganization of the SEI layer, consuming the electrolyte and active lithium, and reducing the theoretical specific capacity; in addition, Mn 2+ Dissolution causes manganese deficiency in the positive electrode, lattice distortion, structural collapse, and decreased stability of the positive electrode active material, thereby reducing the cycle stability of the secondary battery.

[0004] Therefore, it is necessary to provide a secondary battery with both high energy density and high cycle stability. Summary of the invention

[0005] The purpose of the present application is to provide a secondary battery having both high energy density and high cycle stability.

[0006] In a first aspect of the present application, a secondary battery is provided, comprising a positive electrode plate, an electrolyte, a separator and a negative electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active substance, wherein the positive electrode active substance comprises a mixture of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and a manganese ion complexing agent, and wherein the positive electrode plate satisfies the following relationship:

[0007] 0.1≤10000×W1×PD / pH 2 ×W2≤3.0

[0008] Wherein, W1 represents the mass proportion of the manganese ion complexing agent in the positive electrode active material;

[0009] W2 represents the mass proportion of lithium manganese iron phosphate in the positive electrode active material;

[0010] PD g / cm 3 Indicates the compaction density of the positive electrode sheet;

[0011] The pH refers to the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25°C.

[0012] As an embodiment of the present application, the positive electrode sheet satisfies: 0.9≤10000×W1×PD / pH 2 ×W2≤2.1.

[0013] As an embodiment of the present application, the mass proportion W1 of the manganese ion complexing agent in the positive electrode active material satisfies: 0.1%≤W1≤2%.

[0014] As an embodiment of the present application, the mass proportion W2 of lithium manganese iron phosphate in the positive electrode active material satisfies: 10%≤W2≤60%.

[0015] As an embodiment of the present application, the compaction density PD of the positive electrode sheet satisfies: 1.3 g / cm 3 ≤PD≤3.5g / cm 3 .

[0016] As an embodiment of the present application, the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25° C. satisfies: 4≤pH≤8.5.

[0017] As an embodiment of the present application, the manganese ion complexing agent includes at least one of ethylenediaminetetraacetic acid (EDTA), trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (DCyTA), diethyltriaminepentaacetic acid (DTPA), ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA), trisodium salt of hydroxyethyldiaminetetraacetic acid (HEDTA), ethylenediamine, and sulfosalicylic acid.

[0018] As an embodiment of the present application, the chemical formula of the lithium manganese iron phosphate satisfies: LiMn x Fe 1-x PO4, where 0.9 ≥ x ≥ 0.5.

[0019] As an embodiment of the present application, the chemical formula of the lithium nickel cobalt manganese oxide satisfies: LiNi 1-a-b Co a Mn b O2, where 0.3≥a>0, 0.3≥b>0.

[0020] As an embodiment of the present application, the mass ratio of the lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and manganese ion complexing agent is lithium nickel cobalt manganese oxide: lithium iron manganese phosphate: manganese ion complexing agent = (35-90): (10-60): (0.2-2.0).

[0021] As an embodiment of the present application, the positive electrode active material layer further includes a conductive agent and a binder.

[0022] A second aspect of the present application provides an electrical device, wherein the electrical device comprises the secondary battery described in the first aspect of the present application.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] The present application adjusts the manganese ion complexing agent content and acid-base parameters, the content of lithium manganese iron phosphate, and the compaction density of the electrode to satisfy a specific relationship, thereby achieving an optimal ratio combination, and can reduce the dissolution of manganese while ensuring that the active material content is not lost, thereby achieving a stable cycle of the secondary battery. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0029] In a first aspect of the present application, a secondary battery is provided, comprising a positive electrode plate, an electrolyte, a separator and a negative electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active substance, wherein the positive electrode active substance comprises a mixture of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and a manganese ion complexing agent, and wherein the positive electrode plate satisfies the following relationship:

[0030] 0.1≤10000×W1×PD / pH 2 ×W2≤3.0

[0031] Wherein, W1 represents the mass proportion of the manganese ion complexing agent in the positive electrode active material;

[0032] W2 represents the mass proportion of lithium manganese iron phosphate in the positive electrode active material;

[0033] PD g / cm 3 Indicates the compaction density of the positive electrode sheet;

[0034] The pH refers to the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25°C.

[0035] The positive electrode active material of lithium iron manganese phosphate is a powder material and easily absorbs water. When mixed with another positive electrode active material, lithium nickel cobalt manganese oxide (also commonly known as ternary positive electrode material), the ternary positive electrode material, together with the H2O in the lithium iron manganese phosphate and the CO2 in the air, will more easily generate residual alkali (such as Li2CO3 and LiOH) on the surface. These residual alkalis not only increase the pH value of the positive electrode active material, causing the positive electrode slurry to gel during the preparation process, affecting the normal use of the battery electrode, but also have side reactions with the electrolyte during the battery charging and discharging process, causing the battery to swell, affecting the battery's safety performance.

[0036] The present invention comprises a manganese ion complexing agent mixed in the positive electrode active material (including lithium nickel cobalt manganese oxide and lithium manganese iron phosphate) to inhibit the dissolution of Mn 2+ At the same time, the content of manganese ion complexing agent and acid-base parameters, the content of lithium manganese iron phosphate and the compaction density of the pole piece are further adjusted to meet specific relationships, so as to achieve the optimal proportion and reduce the dissolution of manganese ions without losing the content of positive electrode active material, thereby achieving stable cycle of secondary batteries and excellent performance of high energy density.

[0037] Exemplarily, the value of the relationship may be any one of 0.113, 0.293, 0.950, 0.983, 1.286, 1.370, 2.042, and 2.849, or a range between any two values.

[0038] In some embodiments, the positive electrode sheet preferably satisfies: 0.9≤10000×W1×PD / pH 2 ×W2≤2.1.

[0039] In some embodiments, the mass proportion W1 of the manganese ion complexing agent in the positive electrode active material satisfies: 0.1%≤W1≤2.0%. Exemplarily, the value of W1 can be any one of 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 2.0%, or a range between any two values. The manganese ion complexing agent in this application: on the one hand, it can complex with the manganese ions dissolved in the lithium manganese iron phosphate to capture the Mn in the positive electrode sheet. 2+ , reducing side reactions in the electrolyte and improving the cycle performance of the secondary battery; on the other hand, it can also react with the residual alkali in the lithium nickel cobalt manganese oxide ternary material, reducing the content of active residual alkali, thereby reducing the surface pH of the positive electrode active material, and a lower pH is conducive to improving the complex stability between the manganese ion complexing agent and the dissolved manganese ions, further improving the cycle performance of the prepared secondary battery.

[0040] In some embodiments, the mass proportion W2 of lithium manganese iron phosphate in the positive electrode active material satisfies: 10%≤W2≤60%. Exemplarily, the value of W2 can be any one of 10%, 20%, 30%, 40%, 50%, 60% or a range value between any two values. The higher the content of lithium manganese iron phosphate, the higher the energy density of the secondary battery, but the content of dissolved manganese ions is also relatively high, and it will also reduce the compaction density of the positive electrode sheet. After the compaction density is reduced, the reaction activity of the electrolyte and the positive electrode active material will increase. The side reaction of the electrolyte with the dissolved manganese ions and the positive electrode active material will lose the capacity of the battery and destroy the structure of the SEI film of the negative electrode, which is not conducive to the cycle performance of the secondary battery. Therefore, W2 is within the above-mentioned appropriate range, which can make the prepared secondary battery have both high energy density and cycle performance.

[0041] In some embodiments, the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25°C satisfies: 4≤pH≤8.5. The pH value of the complexing agent will affect the complexing effect between the complexing agent and manganese ions. The lower the pH value, the better the stability of the complexing agent and manganese ions, and the better the complexing effect. The pH value is preferably <7; the pH of the manganese ion complexing agent is within the above-mentioned appropriate range, and can have a more stable manganese ion complexing effect while ensuring safety (no acid corrosion occurs inside the battery). Exemplarily, the pH value can be any one of 4.6, 7.4, 8.2 or a range value between any two values.

[0042] In some embodiments, the manganese ion complexing agent includes at least one of ethylenediaminetetraacetic acid (EDTA), trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (DCyTA), diethyltriaminepentaacetic acid (DTPA), ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA), trisodium salt of hydroxyethyldiaminetetraacetic acid (HEDTA), ethylenediamine, and sulfosalicylic acid.

[0043] In some embodiments, the compaction density PD of the positive electrode sheet satisfies: 1.3 g / cm 3 ≤PD≤3.5g / cm 3 The appropriate compaction density can make the secondary battery have both high energy density and cycle stability. For example, the compaction density PD can be 1.3 g / cm 3 , 1.5g / cm 3 , 2.2g / cm 3 , 2.4g / cm 3 , 2.6g / cm 3 、3.1g / cm 3 Any value or a range of values ​​between any two values.

[0044] In some embodiments, the lithium iron manganese phosphate has the following chemical formula: LiMn x Fe 1-x PO4, wherein 0.9≥x≥0.5; wherein x further preferably satisfies x≥0.55. In the positive electrode active material lithium manganese iron phosphate, manganese ions are doped in the iron ion lattice. Therefore, the larger the x value, the higher the proportion of manganese ions. When manganese ions are within the above-mentioned suitable range, the prepared secondary battery can have both higher energy density and improved charge and discharge platform, as well as excellent cycle stability.

[0045] In some embodiments, the lithium nickel cobalt manganese oxide has a chemical formula of: LiNi 1-a-b Co a Mn b O2, where 0.3≥a>0, 0.3≥b>0.

[0046] In some embodiments, the mass ratio of the lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and manganese ion complexing agent is lithium nickel cobalt manganese oxide: lithium iron manganese phosphate: manganese ion complexing agent = (35-90): (10-60): (0.2-2.0). The amount ratio of the positive electrode active material and the manganese ion complexing agent in the positive electrode active material is within the appropriate range, which can fully infiltrate the electrolyte and is conducive to the conduction of active ions, so that the prepared secondary battery has both high energy density and high cycle stability.

[0047] In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder. Common conductive agents and binders in the art can be used in the present application.

[0048] In some embodiments, the conductive agent includes but is not limited to at least one of graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; the binder includes but is not limited to at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer.

[0049] In addition, it should be further explained that the positive electrode sheet of the present application is prepared in the process of preparation according to a method comprising the following steps:

[0050] A manganese ion complexing agent is added to lithium nickel cobalt manganese oxide slurry, and after mixing evenly, lithium iron manganese phosphate slurry is added to obtain a composite active slurry. Finally, the composite active slurry is evenly mixed with a conductive agent and a binder to obtain a positive electrode slurry, and the positive electrode slurry is coated on the surface of the positive electrode collector, and the positive electrode sheet is obtained after drying and compacting.

[0051] Since the manganese ion complexing agent is weakly acidic, it is first added to the lithium nickel cobalt manganese oxide slurry, and through stirring and other processes, the manganese ion complexing agent can be evenly dispersed around the lithium nickel cobalt manganese oxide particles, and the manganese ion complexing agent and the residual alkali on the surface of the lithium nickel cobalt manganese oxide undergo an acid-base neutralization reaction to reduce the pH value of the material surface; and then compounded with the lithium iron manganese phosphate slurry can reduce the influence of the water content of the lithium iron manganese phosphate on the nickel-cobalt-manganese ternary, reduce the gas production of the prepared secondary battery during the cycle process, and improve the safety performance and cycle life of the secondary battery.

[0052] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, a dispersant, and a binder.

[0053] In the present application, the types of the negative electrode current collector and the positive electrode current collector are not specifically limited and can be selected according to actual needs.

[0054] In some embodiments, the negative electrode current collector may preferably use copper foil or carbon-coated copper foil, etc.; the positive electrode current collector may include but is not limited to metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc.; carbon materials such as carbon cloth and carbon paper; composite materials formed by polymers and metal layers. In some embodiments, the positive electrode current collector preferably uses aluminum foil.

[0055] In the secondary battery described in the present application, the type of negative electrode active material is not particularly limited. The negative electrode active material can be at least one of graphite, soft carbon, hard carbon, carbon fiber, silicon-based material, and tin-based material commonly used in the art, but is not limited thereto.

[0056] In the secondary battery described in the present application, the type of the separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride, a spandex film, an aramid film, or a multilayer composite film modified by a coating.

[0057] In the secondary battery described in the present application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0058] In some embodiments, the type of solvent used to form the positive electrode slurry and / or the negative electrode slurry is not limited, as long as it is a solvent that can dissolve or disperse the positive electrode active material, the negative electrode active material, the conductive agent, the binder, and the dispersant.

[0059] In some embodiments, the preparation of a secondary battery includes: stacking the positive electrode sheet, the isolation membrane, and the negative electrode sheet in order, so that the isolation membrane is between the positive and negative electrode sheets to play an isolating role, and then winding them into a square bare cell, loading them into a battery casing, and then baking them at 65 to 95°C to remove water, injecting electrolyte, sealing, and obtaining a secondary battery after standing, hot and cold pressing, formation, clamping, capacity division and other processes.

[0060] The second aspect of the present application provides an electric device, which includes the secondary battery described in the first aspect of the present application. The electric device can be an application device such as a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool. The vehicle can be a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, etc.; the electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, etc. The embodiments of the present application do not impose any special restrictions on the above-mentioned devices.

[0061] The following are specific embodiments of the present application, and the technical scheme of the present application is further described in conjunction with the embodiments, but the present application is not limited to these embodiments. The reagents, methods and equipment used in the present application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0062] Example 1

[0063] A secondary battery is provided, wherein a method for preparing the secondary battery comprises the following steps:

[0064] Positive electrode preparation

[0065] The positive electrode active material, conductive carbon black, adhesive PVDF, and manganese ion complexing agent (EDTA) in the positive electrode slurry are mixed in a weight ratio of 96.2:2.0:1.8. The positive electrode active material includes (LMFP)LiMn 0.6 Fe 0.4 PO4, nickel cobalt manganese oxide (NCM622, chemical formula LiNi 0.6 Co 0.2 Mn 0.2 O2) and a manganese ion complexing agent, the specific weight percentages are shown in Table 1, and the specific mixing process is: first dissolve lithium nickel cobalt manganese oxide in a solvent NMP in a planetary mixer, then add the manganese ion complexing agent, pre-disperse for 5 minutes, then add lithium manganese iron phosphate and stir for 20 minutes, finally add a binder and a conductive agent while mixing and stirring, add NMP according to the viscosity of the out-of-pot, adjust the viscosity of the positive electrode slurry to within the range of 5000-6000mPa·s, and then perform vacuum to eliminate bubbles to obtain the positive electrode slurry;

[0066] The prepared positive electrode slurry was sieved using a 150-mesh double-layer filter cloth, and the filtrate was coated on both sides of a 12 μm aluminum foil (coating amount was 20 g / cm 2 ), heated and dried in an oven, cold pressed (pressure of 4.2 MPa), cut into strips to obtain positive electrode sheets. The parameters of the positive electrode sheets are detailed in Table 1;

[0067] Negative electrode sheet preparation

[0068] The upper negative electrode active material graphite, conductive agent carbon black, binder styrene-butadiene rubber and additive sodium carboxymethyl cellulose were mixed in a mass ratio of 96.5:0.7:1.8:1.0, and deionized water was added as a solvent. After stirring evenly under the action of a vacuum mixer, a negative electrode slurry was obtained; the negative electrode slurry was evenly coated on both sides of the double surface of the 6μm negative electrode collector copper foil, heated and dried in an oven, cold pressed, and cut into strips to obtain a negative electrode sheet. The compaction density of the negative electrode sheet was 1.60g / cm 3 ;

[0069] Electrolyte preparation

[0070] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed organic solvent, and then LiPF6 is dissolved in the mixed organic solvent, and after mixing evenly, an electrolyte with a lithium ion concentration of 1 mol / L is obtained;

[0071] Assembly of secondary batteries

[0072] The prepared positive electrode sheet, separator (polypropylene separator, Enjie BP129B), and negative electrode sheet are stacked in order so that the separator is between the positive and negative electrode sheets, and then wound into a battery cell. After the winding is completed, the pole ears are welded and then placed in the shell; the electrolyte is injected into the shell, and then a secondary battery is formed through packaging, standing, formation, aging, shaping and other processes.

[0073] Examples 2-11, Comparative Examples 1-3

[0074] A series of secondary batteries are provided, which are prepared by referring to the preparation method of Example 1. The difference from Example 1 is that the type and ratio of raw materials of the positive electrode slurry are adjusted to prepare positive electrode plates with different parameters. The other parameters are the same as those of Example 1. The specific parameters of the positive electrode plates are detailed in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] In Table 1, (1) the compaction density of the negative electrode sheet is obtained by dividing the surface density by the thickness;

[0079] (2) The pH value of the manganese ion complexing agent in a saturated aqueous solution at 25°C is tested using a hydrogen ion electrode method. The specific test steps include: immersing a hydrogen ion electrode in a saturated aqueous solution (25°C) containing the manganese ion complexing agent, and calculating its pH value based on the potential signal.

[0080] Electrochemical performance test

[0081] The electrochemical cycle performance of the secondary batteries prepared in the above examples and comparative examples was tested, and the specific testing method is as follows:

[0082] (1) Energy density: Weigh the secondary battery first, then charge it at 0.33C constant current and constant voltage at 25°C to 4.25V, with a cut-off current of 0.05C; then, after standing for 30 minutes, discharge it at 0.33C constant current to 2.8V, and record the discharge capacity and energy of the secondary battery; Energy density = discharge energy / weight of the secondary battery;

[0083] (2) Charge and discharge platform voltage: platform voltage = discharge energy / discharge capacity;

[0084] (3) Cycle stability: The secondary battery was placed in a charge and discharge test cabinet at a constant temperature of 25°C, with a charge rate of 1C and a discharge rate of 1C. The capacity retention rate after 200 cycles was calculated. The positive electrode sheet of the secondary battery was disassembled and dissolved with a 0.1 mol / L HCl aqueous solution. The amount of manganese ions in the HCl solution was tested with AAS. The test results are shown in Table 2.

[0085] Table 2

[0086]

[0087] From the above results, we can see that:

[0088] By adjusting the manganese ion complexing agent content and acid-base parameters, the content of lithium manganese iron phosphate, and the compaction density of the electrode to meet specific relationships, the optimal ratio can be achieved, and the dissolution of manganese can be reduced while ensuring that the active material content is not lost, thereby achieving a stable cycle of the secondary battery.

[0089] Among them, the energy density of the secondary batteries prepared in the present application is above 220Wh / kg; the charge and discharge platform voltage is above 3.5V; the capacity retention rate after 200 charge and discharge cycles at 1C is above 92%, and the manganese ion dissolution amount is low, all below 10mg / L.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, an electrolyte, a separator and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises a mixture of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and a manganese ion complexing agent, characterized in that: The positive electrode sheet satisfies the following relationship: 0.1≤10000×W1×PD / pH 2 ×W2≤3.0 Wherein, W1 represents the mass proportion of the manganese ion complexing agent in the positive electrode active material; W2 represents the mass proportion of lithium manganese iron phosphate in the positive electrode active material; PD g / cm 3 Indicates the compaction density of the positive electrode sheet; The pH refers to the pH value of the manganese ion complexing agent in a saturated aqueous solution at 25°C.

2. The secondary battery according to claim 1, characterized in that: The positive electrode sheet meets the following conditions: 0.9≤100*W1×PD / pH 2 ×W2≤2.

1.

3. The secondary battery according to claim 1, characterized in that: The mass proportion W1 of the manganese ion complexing agent in the positive electrode active material satisfies: 0.1%≤W1≤2%.

4. The secondary battery according to claim 1, characterized in that: The mass proportion W2 of lithium manganese iron phosphate in the positive electrode active material satisfies: 10%≤W2≤60%.

5. The secondary battery according to claim 1, characterized in that: The compaction density PD of the positive electrode sheet satisfies: 1.3 g / cm 3 ≤PD≤3.5g / cm 3 .

6. The secondary battery according to claim 1, characterized in that: The pH value of the manganese ion complexing agent in a saturated aqueous solution at 25° C. satisfies: 4≤pH≤8.

5.

7. The secondary battery according to claim 1, characterized in that: The secondary battery satisfies at least one of the following characteristics: (1) the manganese ion complexing agent includes at least one of ethylenediaminetetraacetic acid, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, diethyltriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, trisodium salt of hydroxyethyldiaminetetraacetic acid, ethylenediamine, and sulfosalicylic acid; (2) The chemical formula of the lithium manganese iron phosphate satisfies: LiMn x Fe 1-x PO4, where 0.9 ≥ x ≥ 0.5; (3) The general chemical formula of the lithium nickel cobalt manganese oxide satisfies: LiNi 1-a-b Co a Mn b O2, where 0.3≥a>0, 0.3≥b>0.

8. The secondary battery according to claim 1 or 7, characterized in that: The mass ratio of the lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and manganese ion complexing agent is lithium nickel cobalt manganese oxide: lithium iron manganese phosphate: manganese ion complexing agent = (35-90): (10-60): (0.2-2.0).

9. The secondary battery according to claim 1, characterized in that: The positive electrode active material layer also includes a conductive agent and a binder.

10. An electrical device, characterized in that: The electrical device comprises the secondary battery according to any one of claims 1 to 9.

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